ACTION OF WATER ON NITROGEN TRIOXIDE. 197 



It would be the same with the metamorphosis of nitrogen 

 monoxide into nitric oxide 



N 2 + = 2NO, 



if it could occur. In reality, this reaction does not take place 

 directly, being endothermal. But (pp. 192 and 194) the real 

 existence of the inverse decomposition, which presents an 

 anomaly of the same order and correlative, has been established, 

 viz. a simple gaseous decomposition effected with contraction: 

 four volumes being changed into three. The relation is more 

 clearly defined than the first, if not in principle, at least in fact, 

 seeing that it occurs between three gases of which the density 

 is known. If nitric peroxide is the final stage of oxidation of 

 anhydrous nitrogen trioxide by free oxygen, it is not the same 

 with nitrogen trioxide dissolved in water; for dilute solutions of 

 nitrogen trioxide gradually absorb free oxygen, and become 

 gradually changed into nitric acid: N 2 3 + H 2 -h 2 = 2HN0 3 

 dilute liberates -j-18'5. If ozone be substituted for oxygen the 

 oxidation of the nitrogen trioxide is instantaneous. 



We now return to the action of water on nitrogen trioxide. 

 In presence of water the anhydrous acid becomes wholly or in 

 part hydrated nitrogen trioxide; it also shows a tendency to 

 decompose into nitric acid and nitric oxide. The reaction 

 3NA gas + water = 2HN0 3 dilute + 4NO liberates + 44. 

 But this last reaction only takes place to any appreciable 

 extent if water be present in sufficient quantity. In this case 

 it is partially decomposed into nitric oxide and oxygen, which 

 gradually transforms another portion of nitrogen trioxide into 

 nitric acid. This may be observed by treating solutions of 

 barium nitrite of various degrees of concentration with dilute 

 sulphuric acid. The immediate reaction here attributed to 

 nascent oxygen is the same as the slow reaction of free oxygen 

 on dissolved nitrogen trioxide. 



From the well-known reaction of water on anhydrous nitrogen 

 trioxide, and from experiments on the distribution of baryta 

 among dilute hydrochloric and acetic acid and nitrogen trioxide, 

 the author is of opinion that a double dissociation is observed 

 when nitrogen trioxide is in presence of an insufficient quantity 

 of water, viz. the dissociation of the hydrated nitrogen trioxide, 

 which is partly changed into water and anhydrous acid, and the 

 dissociation of the anhydrous nitrogen trioxide, which is partly 

 changed into oxygen and nitric oxide. The effects are moreover 

 complicated by the ulterior action of the oxygen which dis- 

 appears in transforming another portion of the nitrogen trioxide 

 into nitric acid. 



Under these conditions, the nitric oxide being eliminated 

 as produced, it would seem as if its formation should be in- 

 definitely reproduced. 



